U.S. patent number 6,935,103 [Application Number 10/372,659] was granted by the patent office on 2005-08-30 for device for exhaust-gas purification, and an operating and monitoring for said device.
This patent grant is currently assigned to DaimlerChrysler AG, PURem Abgassysteme GmbH & Co. KG. Invention is credited to Klaus Binder, Peter Ebel, Gerhard Fraenkle, Alexander Funk, Georg Huthwohl, Klaus-Juergen Marquardt, Bernd Maurer, Ansgar Schaefer.
United States Patent |
6,935,103 |
Binder , et al. |
August 30, 2005 |
Device for exhaust-gas purification, and an operating and
monitoring for said device
Abstract
A device for exhaust-gas purification utilizes reduction of
nitrogen oxides which are present in the exhaust gas from internal
combustion engines by way of gaseous ammonia with an SCR catalytic
converter. The functions of the device are monitored with regard to
their line paths with connections, valves and sensors by referring
to these elements themselves using suitable control circuitry via
the evaluation and control unit.
Inventors: |
Binder; Klaus (Deizisau,
DE), Ebel; Peter (Braunsbach, DE),
Fraenkle; Gerhard (Remshalden-Grunbach, DE), Funk;
Alexander (Altbach, DE), Marquardt; Klaus-Juergen
(Remshalden, DE), Schaefer; Ansgar (Ehningen,
DE), Huthwohl; Georg (Soest, DE), Maurer;
Bernd (Balve, DE) |
Assignee: |
DaimlerChrysler AG (Stuttgart,
DE)
PURem Abgassysteme GmbH & Co. KG (Menden,
DE)
|
Family
ID: |
28458328 |
Appl.
No.: |
10/372,659 |
Filed: |
February 25, 2003 |
Foreign Application Priority Data
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Feb 25, 2002 [DE] |
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102 07 984 |
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Current U.S.
Class: |
60/286; 60/274;
60/303; 60/295; 60/301 |
Current CPC
Class: |
F01N
3/2066 (20130101); F01N 2610/02 (20130101); Y02A
50/20 (20180101); Y02A 50/2325 (20180101); Y02T
10/24 (20130101); F28D 15/02 (20130101); Y02T
10/12 (20130101) |
Current International
Class: |
F01N
3/20 (20060101); F01N 003/00 () |
Field of
Search: |
;60/274,286,295,301,303 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Denion; Thomas
Assistant Examiner: Tran; Diem
Attorney, Agent or Firm: Crowell & Moring LLP
Claims
What is claimed is:
1. A device for exhaust-gas purification involving reduction of
nitrogen oxides, which are present in the exhaust gas from internal
combustion engines, comprising an SCR catalytic converter using
ammonia, at least one pressure vessel having a filling which
releases gaseous ammonia when heat is supplied, and a metering unit
downstream of the pressure vessel in a transition to the SCR
catalytic converter, which metering unit is an ammonia source,
wherein the pressure vessel filling is liquid ammonia, and at least
the metering unit is arranged in a gastight, pressure-monitored
housing.
2. The device as claimed in one claim 1, wherein a heater is
arranged at least one of detachably and separately with respect to
the pressure vessel.
3. The device as claimed in claim 1, wherein the pressure vessel is
exchangeable.
4. The device as claimed in claim 1, wherein a heat exchanger,
which is configured to be fed with waste heat from an internal
combustion engine, is operatively associated with the vessel.
5. The device as claimed in claim 4, wherein the heat exchanger is
heated from a cooling circuit of the internal combustion
engine.
6. The device as claimed in claim 5, wherein the heat exchanger is
connected to the cooling circuit of the internal combustion
engine.
7. The device as claimed in claim 4, wherein the heat exchanger is
heated by exhaust gas from the internal combustion engine.
8. The device as claimed in claim 7, wherein the heat exchanger is
heated by at least one of heat conduction and heat radiation.
9. The device as claimed in claim 4, wherein the heat exchanger is
a heat pipe.
10. The device as claimed in claim 4, wherein a predetermined limit
temperature of the pressure filling limits heating capacity which
is introduced.
11. The device as claimed in claim 1, wherein the pressure vessel
is operatively associated with an electrical heater.
12. The device as claimed in claim 11, wherein the pressure vessel
is heated by heating elements which lie at least one of inside and
outside thereof.
13. The device as claimed in claim 11, wherein the pressure vessel
is heated by a radiant heater.
14. The device as claimed in claim 11, wherein an inductive heater
is provided for the pressure vessel filling.
15. The device as claimed in claim 1, wherein the pressure vessel
is operatively associated with a holding vessel.
16. The device as claimed in claim 15, wherein the holding vessel
is a heat exchanger.
17. The device as claimed in claim 15, wherein the holding vessel
is of gastight construction.
18. The device as claimed in claim 15, wherein the holding vessel
is of insulated construction.
19. The device as claimed in claim 15, wherein the holding vessel
has a vessel opening which is selectively openable to atmosphere
and to be blocked off.
20. The device as claimed in claim 1, wherein the at lease one
pressure vessel consists of a plurality of pressure vessels.
21. The device as claimed in claim 20, wherein the pressure vessels
are each operatively arranged in a holding vessel.
22. The device as claimed in claim 20, wherein the pressure vessels
are arranged operatively in a common holding vessel.
23. The device as claimed in claim 20, wherein the pressure vessels
are jointly operatively connected to the metering unit.
24. The device as claimed in claim 20, wherein the pressure vessels
are separately operatively connected to the metering unit.
25. The device as claimed in claim 20, wherein the pressure vessels
are switchably operatively connected to the metering unit.
26. The device as claimed in claim 1, wherein the pressure vessel
is operatively associated with a line-break safety device and,
downstream of the latter, a vessel valve.
27. The device as claimed in claim 26, wherein the metering unit
and the vessel valve arranged on an outlet side of the pressure
vessel, are located in the metering unit.
28. The device as claimed in claim 1, wherein the metering unit is
operatively connected downstream of the pressure vessel in a
direction of the catalytic converter and comprising, in a direction
of passage, a shut-off valve, a temporary store and a metering
valve, having pressure recording provided on both sides
thereof.
29. The device as claimed in claim 28, wherein a pressure sensor
for pressure recording is provided on sides of the metering
valve.
30. The device as claimed in claim 28, wherein a temperature sensor
is provided between the temporary store and the metering valve.
31. The device as claimed in claim 30, wherein the temperature
sensor is arranged downstream of the pressure sensor which is
mounted upstream of the metering valve.
32. The device as claimed in claim 28, wherein a temperature sensor
is arranged on both sides of the metering valve.
33. The device as claimed in claim 28, wherein the shut-off valve
and metering valve are as controllable valves.
34. A method for operating a device for exhaust-gas purification
involving reduction of nitrogen oxides which are present in the
exhaust gas from a motor vehicle internal combustion engine, having
an SOR catalytic converter using ammonia, at least one pressure
vessel having a filling which releases gaseous ammonia when heat is
supplied, a metering unit located downstream of a the pressure in a
transition to the SCR catalytic converter and a temporary store
(18) located between a shut-off valve and a metering valve,
comprising alternatively filling the temporary store in a
pressure-limited manner, from the pressure vessel when the metering
valve is closed and then emptying the temporary store via the
metering valve down to a minimum pressure when the shut-off valve
is closed, wherein when the internal combustion engine is being
switched off, the temporary store is emptied to a exhaust section
of the internal combustion engine.
35. The method as claimed in claim 34, wherein the exhaust section
includes said SCR catalytic converter.
36. A method for monitoring a device for exhaust-gas purification
involving reduction of nitrogen oxides which are present in exhaust
gas from a motor vehicle internal combustion engine, wherein the
device has an SCR catalytic converter using ammonia, at least one
pressure vessel having a filling which releases gaseous ammonia
when heat is supplied, and a metering unit downstream of the
pressure vessel in a transition to the SCR catalytic converter,
which metering unit is an ammonia source, wherein the pressure
vessel filling is liquid ammonia, and at least the metering unit is
arranged in a gastight, pressure-monitored housing, comprising
processing pressure values obtained from a pressure recording in
the metering unit, and a housing which surrounds the metering unit
in an evaluation and control unit and converting the processed
pressure values into control signals for at least one of valves,
heater and warning signals.
37. The method as claimed in claim 36, wherein, in the event of a
limit pressure being exceeded in a space surrounded by the housing
and holding a vessel valve, a shut-off valve and the metering
valve, the vessel valve is closed and, if the pressure limit
continues to be exceeded, a line-pressure safety feature is
activated.
38. The method as claimed in claim 36, wherein, to check for leaks
in a metering line leads from a metering valve to an exhaust
section of the internal combustion engine, exhaust-gas back
pressure on a side of the internal combustion engine is compared
with a pressure on the a side of metering valve.
39. The method as claimed in claim 38, further comprising to check
sealing the metering valve, filling the temporary store between
shut-off valve and metering valve, and checking that the pressure
remains constant when the valves are closed.
40. The method as claimed in claim 38, further comprising, to test
a pressure sensor located upstream of a metering valve, observing a
pressure curve of the pressure sensor during filling of the
temporary store for correlation with a pressure curve stored in the
evaluation and control unit.
41. The method as claimed in claim 38, wherein the pressure on the
metering valve side is recorded by a pressure sensor arranged
downstream of the metering valve.
42. The method as claimed in claim 41, wherein, to check
correctness of the pressure determined by the pressure recording
arranged downstream of the metering valve, the determined pressure
is compared with the exhaust-gas back pressure when the metering
valve is closed.
43. The method as claimed in claim 41, further comprising, in the
event of a fault, at least one of closing the pressure valve and
emitting a warning signal.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a device for exhaust-gas
purification involving reduction of nitrogen oxides, which are
present in the exhaust gas from internal combustion engines, in
particular for motor vehicles, by way of ammonia in an SCR
catalytic converter, and to a method for operating and monitoring a
device of this type.
Devices which operate with SCR catalytic converters (Selective
Catalytic Reduction catalytic converters), are disclosed, for
example, in DE 297 08 591 U1. Particularly when used in motor
vehicles, devices of this type have to satisfy particular demands
with regard to the space taken up, the ability for spontaneous
response and the ability to adapt to constantly changing working
conditions, as well as operational safety.
In connection with operation safety, substances or substance
mixtures which release ammonia through thermolysis are used as the
ammonia source, which has the effect of requiring an increased
amount of space, because the ammonia which can be used for the
reduction constitutes only a fraction of the starting material.
Moreover, spontaneous response requires a sufficiently large
reservoir or temporary store volume for the ammonia which has been
released in gas form. All this is associated with corresponding
safety requirements.
SUMMARY OF THE INVENTION
An object of the present invention is to form a device such that,
with a minimum demand for space, a spontaneous ability to respond
and the required operational safety are provided.
This has been achieved by a pressure vessel, which has a filling
which releases ammonia in gas form when heat is supplied and
downstream of which in the transition to the catalytic converter,
there is a metering unit is provided as ammonia source, wherein the
pressure vessel has, as its filling is liquid ammonia, and in that
at least the metering unit is arranged in a gastight,
pressure-monitored housing. Accordingly, the ammonia is stored in
liquefied form in the pressure vessel and the metering unit for the
ammonia which has been converted into gas form is arranged in a
substantially gastight, pressure-monitored housing. Thereby, with a
high useful volume of the device, controlled metering is possible,
combined, at the same time, with monitoring of operation for
operational safety. In this way, it is also now possible, in
particular, to produce separate safety features for the pressure
vessel, on one hand, and the further connections, as is expedient
with a view to the pressure vessel being designed as an
exchangeable pressure cylinder. Moreover, it is, in a simple way,
possible to assign the pressure vessel a heat exchanger for heating
purposes and for this heat exchanger, if appropriate, to be
configured as an insulating and/or pressure-resistant holding
vessel, so that the holding vessel can in effect make the pressure
vessel into a double-walled design.
In conjunction with a configuration of this type, when the heat
exchanger is heated with waste heat from the internal combustion
engine, the holding vessel can be provided so as to surround the
corresponding heater, or it is also contemplated, given a suitable
configuration, for the heater to be integrated in the holding
vessel. In the latter case, the evaporation of the ammonia stored
in liquid form in the pressure vessel is controlled via a
controlled introduction of heat. Furthermore, with a view to making
the temperature of the pressure vessel or its filling more uniform
when the internal combustion engine is not operating, the holding
vessel offers favorable conditions, in particular also with a view
to maintaining a minimum temperature, if appropriate by
heating.
To achieve a high degree of flexibility in terms of the heating
power which can be applied, it may be expedient for a plurality of
types of heating to be provided in combination, for example heating
by use of the waste heat from the internal combustion engine from
the cooling circuit and from the exhaust gas, and if appropriate
also by use of an independent electrical heater. In particular, for
the introduction of heat from the exhaust gas, the heat transfer
can also be effected via heat pipes, especially as these offer
favorable heat transfer conditions with regard to defining limit
temperatures.
If the holding vessel is, as is preferred, configured to be
substantially gastight, and if appropriate also insulating, it may
be expedient for it to be assigned a vessel opening which opens to
atmosphere and can be blocked off and which may be controlled in
particular as a function of temperature, even automatically, for
example by thermocouples or bimetallic elements, in order, if
necessary, to be able to combat excessive heating. Moreover, the
holding vessel, in particular in its insulating configuration, may
also form a safety vessel.
Within the context of the present invention, it may be expedient to
operate with a plurality of pressure vessels, in particular in the
form of exchangeable pressure vessels, which are preferably each
arranged in holding vessels which can be heated independently, it
being contemplated for these vessels to be combined to form a
single unit. Dividing up the store of reducing agent which is
carried in this way makes it possible to provide the reducing agent
in units which are easy to handle and can be connected up
separately or together, including, if appropriate, in terms of the
heating. Thereby, rapid response can be achieved by the device even
when little energy is being used and the overall storage volume is
large.
To achieve priority heating of the filling of the pressure
vessel(s) in braking and overrun mode of the associated internal
combustion engine, it is further contemplated that the
corresponding actuation takes place on the basis of information
provided via the engine management system.
Exchangeable pressure vessels, in particular in cylinder form,
which can be used in the context of the invention are preferably
provided, in a known way, with a line-break safety feature and,
downstream of the latter, a vessel valve. The vessel valve is
expediently also surrounded by the housing of the metering unit, so
that it is possible to carry out monitoring functions with regard
to possible leaks, and if appropriate also malfunctions on the part
of the metering unit, given suitable control technology links, and
this includes monitoring functions with regard to the functions of
the metering unit itself.
The metering unit which can be used in the context of the
invention, but also in general terms where the reducing agent is
introduced into the catalytic converter in gas form, has, despite
its apposite, versatile functions, a simple structure. Starting
from the vessel valve, in the direction of passage, the meter unit
comprises a shut-off valve, a temporary store and a metering valve,
with pressure recording provided on both sides of the metering
valve, in particular by way of pressure sensors. It is deemed
currently preferable for a temperature sensor to be arranged
downstream of the pressure sensor which is mounted upstream of the
metering valve and for its part lies downstream of the temporary
store.
In particular, within the context of the present invention, it is
also contemplated for the pressure difference occurring at the
metering valve--as a throttle--to be utilized, on account of the
evolution of heat which occurs correspondingly to the pressure
drop, to replace one of the pressure sensors used as a pressure
pick-up with a temperature pick-up, in accordance with the
following law ##EQU1##
especially as the device according to the invention for exhaust-gas
purification is in any event assigned an electronic evaluation and
control unit which monitors the filling level of the pressure
vessel(s) and controls the metering unit and monitors it for leaks
and operating defects. Using a temperature pick-up instead of a
pressure pick-up further simplifies and reduces the cost of the
device.
With a view to monitoring leaks from the metering unit, according
to the invention, it is deemed currently preferable for the housing
of the metering unit also to be assigned a pressure sensor.
Thereby, so that all the individual elements of the metering unit,
for example in particular including the connected lines, can be
monitored for any leaks to atmosphere.
Irrespective of a supply of gaseous ammonia via the pressure
vessel, which is preferably controlled as a function of the
operating conditions of the internal combustion engine, it is
impossible to avoid pressure fluctuations which, by acting on the
metering valve, would adversely affect operation of the latter.
According to the present invention, these fluctuations can be
compensated for by the temporary store interacting with the
shut-off valves. In addition, the temporary store also gives
advantageous options with regard to the monitoring and functional
testing of the system.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, advantages and novel features of the present
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings.
The sole figure schematically shows an embodiment of the present
invention in which an internal combustion engine in particular a
diesel internal combustion engine is used as the drive source of a
motor vehicle, and is assigned a control unit via which the engine
functions are controlled in a known way as a function of
characteristic variables recorded at the vehicle and/or at the
engine.
DETAILED DESCRIPTION OF THE DRAWING
To discharge the exhaust gases, an internal, combustion engine 1 is
assigned an exhaust section 3, in which there is what is known as
an SCR catalytic converter 4 for reducing the nitrogen oxides with
are present in the exhaust gases. The catalytic converter 4 is
acted on by gaseous ammonia as reducing agent. The supply of
gaseous ammonia to the catalytic converter 4 is metered via a
metering line 5, which in the diagrammatic illustration opens out
into the exhaust section 3 upstream of the catalytic converter
4.
The metering line 5 is located in a transition to a metering unit
6, in which the ammonia, which is initially in liquid form in a
pressure vessel 7, after a suitable proportion has been converted
into the gaseous state by heating, is metered in accordance with
the prevailing exhaust-gas conditions, which are dependent on the
operating conditions of the internal combustion engine 1. For this
purpose, the metering unit 6 is assigned an evaluation and control
unit 8, in which relevant data relating to the exhaust-gas
purification device, which is denoted generally by numeral 9, are
linked to operating data of the internal combustion engine,
recorded by a control unit 2, and are converted into control
commands for the metering unit 6 and, if necessary, for the heating
of the pressure vessel 7 and/or its filling.
In addition, the evaluation and control unit 8 allows actuation of
the elements of the metering unit 6 such that the device 9, in
particular the metering unit 6, can be checked in terms of its
functions and also as to whether there are any links which could
have an adverse effect on the functional reliability and operating
safety of the device 9. The sole FIGURE only indicates the contours
of the catalytic converter 4, because its structure corresponds to
known embodiments.
The illustration of the pressure vessel 7 is also only shown
schematically, from which it can be seen that the pressure vessel
7, for example a conventional pressurized cylinder, is arranged
inside a holding vessel 10, which surrounds the pressure vessel 7,
preferably in a pressure-tight manner. It is also contemplated that
the holding vessel 10 form an insulating and/or heating casing
which, if appropriate, is responsible for heat exchanger functions
or is assigned heat-conducting devices which allow the pressure
vessel 7 to be heated by externally supplied heat.
In this context, it is contemplated, for example, as indicated by
the arrow 11, for exhaust-gas heat to be used to heat the pressure
vessel 7 and/or its filling or contents, it being possible for heat
transfer to be effected, for example, from the exhaust section 3 to
the pressure vessel 7 via heat pipes which pass through the holding
vessel 10. It is also contemplated for the heating to be carried
out by heater coils which are assigned to the holding vessel 10 and
for their part (not shown) are supplied from the cooling-water
circuit of the internal combustion engine 1.
Furthermore, it is possible, by way of example, for electrical
heater coils to be arranged as radiant heaters within the holding
vessel 10 or to provide an inductive heater and therefore for
heating devices (not shown) to be actuated with a view to
maintaining limit temperatures and/or currently desired heating
temperatures, if appropriate as a function of other parameters, by
way of the evaluation and control unit 8. For example, in the case
of electrical heating, this heating can be switched on and off or
its heating power be controlled appropriately, or, heating from the
cooling circuit, to influence the quantity of cooling water flowing
through.
Depending on its particular configuration, the holding vessel 10
may also be configured as a double shell with respect to the
pressure vessel 7, irrespective of the functions which have been
discussed above. Thereby, an additional safety feature for the
pressure vessel 7 can be produced, in combination, for example,
with monitoring of the pressure vessel 7 for possible leaks via
sensors which respond to the corresponding substance of the filling
of the pressure vessel, in the exemplary embodiment ammonia, and
for their part are in turn linked to the evaluation and/or control
unit 8, so that corresponding warning signals can be triggered.
This is also contemplated with a view toward temperature monitoring
of the pressure vessel 7 with the embodiment shown also offering
the option, with regard to the holding vessel 10, of assigning the
pressure vessel 7, for example, a connection to atmosphere which is
controlled as a function of temperature, as indicated by numeral
12. The reference numeral 13 indicates that the pressure vessel 7
is provided on the outlet side with a line-break safety feature
which, in a similar way to known line-break safety features used in
the domestic sector, responds when a quantity of gas which is
greater than the maximum discharge quantity required in operation
flows out.
The line-break safety feature 13 is adjoined by the vessel valve
14, which is likewise only schematically shown and by way of which
the connection between pressure vessel 7 and metering unit 6 is
produced. The vessel valve 14 has its connection part to the
pressure vessel 7 or an associated connection stub located within
the housing 15 of the metering unit 6, so that a substantially
gastight holder for connections, screw joints and attachment device
for the metering unit 6, which can be continuously monitored for
any leaks, is created by the housing 15, (which is indicated
schematically by dot-dashed lines.) For this purpose, the housing
15, is assigned a pressure sensor 16.
The metering unit 6 furthermore comprises, in succession in the
following order downstream in the direction of the exhaust section,
a shut-off valve 17, a temporary store 18, a first pressure sensor
19, a temperature sensor 20, a metering valve 21 and a second
pressure sensor 22. Shut-off valve 17 and metering valve 21 are
controlled, in particular magnetically actuated valves which are
actuated by the evaluation and control unit 8. The sensors 19, 20
and 22 are also connected in a corresponding way to the evaluation
and control unit 8.
When the vessel valve 14 and shut-off valve 17 are open, the
temporary store 18 is filled with gaseous ammonia in accordance
with the filling of the pressure vessel 7 with ammonia, and the
quantity of gas which has in each case been predetermined by the
evaluation and control unit 8 and is fed to the exhaust section 3
via the metering line 5, is metered in via the metering valve 21.
The sensors 19, and 22 are used for pressure monitoring, allowing
the volumetric flow to be controlled in accordance with the
resulting pressure drop and also allowing a corrective adjustment
to the volumetric flow as a result of feedback to the metering
valve 21.
The conditions for a relatively low, uniform application of
pressure to the metering valve 21, which is matched to the function
of the metering valve 21, are ensured by the temporary store 18 as
a result of the temporary store 18 alternately being filled with
gaseous ammonia when the shut-off valve 17 is open and the metering
valve 21 is closed. Then, when the shut-off valve 17 is closed,
emptying to the metering line 5 or into the exhaust section 3 can
take place within relatively tight pressure limits via the metering
valve 21, until a certain minimum pressure has been reached.
Thereupon, the temporary store 18 is filled again.
If operation of the vehicle ceases as a result of the internal
combustion engine 1 being turned off, it is preferable for the
temporary store 18 likewise to be emptied via the metering valve 21
to the exhaust section 3. For subsequent restarting of the internal
combustion engine 1, there is therefore an accumulation of ammonia
in the catalytic converter 4, allowing the latter to respond
rapidly even in situations in which, on account of the ambient
temperatures, a certain run-up time for the heater is required
before gaseous ammonia can be produced, unless, in conjunction with
the insulating configuration of the holding vessel 10, the latter
is held, even for a limited time, at a certain minimum temperature,
which is likewise contemplate within the scope of the
invention.
The exemplary embodiment illustrates just one pressure vessel 7
arranged in a holding vessel 10. As an alternative, it is also
contemplated for a plurality of pressure vessels 7 to be provided
in a similar arrangement and configuration. The pressure vessels
can be connected to the metering unit 6 individually or in
combination, parallel connection to the metering unit 6 expediently
being provided with a view to making the cylinders suitably
exchangeable. Thereby, the pressure vessels 7 can be changed even
during operation. The use of a plurality of pressure vessels 7
arranged individually or together in one or more holding vessels 10
also makes it possible to use the pressure vessels 7 alternately to
feed the catalytic converter, in order, for example, to be able to
compensate for temperature-related fluctuations in the production
of gas of the individual pressure vessel 7 by in each case
connecting up another pressure vessel.
Despite the simple structure of the metering unit 6, it offers
extensive possibilities for leak detection and monitoring of its
elements with regard to their functions, for example with regard to
functional monitoring of the sensors and checking the seal of the
valves. The corresponding test sequences can be initiated and
carried out automatically, at predetermined time intervals, by the
evaluation and control unit 8 and corresponding malfunctions can be
recorded, indicated and limited in terms of any damaging effects
which they may have by switching off or switching over to emergency
operation.
It has already been noted that leaks inside the metering unit 6 as
a whole can be recorded by the pressure sensor 16, which may to
this end also be replaced by a sensor means which records the
corresponding concentration of ammonia. Furthermore, it is within
the scope of the present invention to use a test sequence which
detects leaks between vessel valve 14, including leaks from the
valve 14 and from the valve connection, and shut-off valve 17 by
closing the shut-off valve 17 when the vessel valve 14 is open and
using the sensor 16 to monitor the pressure within the housing 15
to observe whether a limit value is exceeded. A corresponding
option consists in recording the time-dependent changes in the
pressure.
If a leak is detected, when appropriately confirmed by the
time-dependent monitoring, the vessel valve 14 is closed and the
shut-off valve 17 and the metering valve 21 are preferably opened,
in order to remove gas from the unit and to use the residual gas
for the reduction. In a corresponding way, leaks can be detected
between shut-off valve 17 and metering valve 21, specifically, when
the above-mentioned valves are closed and the temporary store 18 is
filled, by the pressure sensor 19 which lies in this region or also
by recording pressure changes in the interior of the housing 15 by
the sensor 16.
A simplified sequence for recording the entire section between
vessel valve 14 and metering valve 21 checking the entire section
and localizing the check in the manner described above only if a
leak is detected.
Finally, leaks can be detected downstream of the metering valve 21,
including the region of the metering line 5, all the way into the
exhaust section 3, or a break in the metering line 5, specifically
by the pressure recorded by the pressure sensor 22 located
downstream of the metering valve 21. If this pressure is virtually
constant when the metering valve 21 is closed and is not correlated
with the exhaust-gas back pressure measured in the exhaust section
3 upstream of the catalytic converter 4, this is a clear indication
of a corresponding fault. As a result, the shut-off valve 17 or the
vessel valve 14 needs to be closed and a corresponding warning
message needs to be signaled.
Therefore, within the scope of the present invention, the
leaktightness of the device 9 can be monitored with little outlay
and virtually continuously, and therefore high operational
reliability can be ensured, especially since corresponding
irregularities can be recorded and processed using the diagnosis
systems which are in any case present in vehicles. The monitoring
reliability in this respect can be improved still further by the
holding vessel 10 together with the pressure vessel 7 and the
metering unit 6 as a whole being arranged within a substantially
gastight and preferably also protective enclosure which, as has
been outlined above, may if appropriate be included in the sensor
monitoring system.
In addition to the leak monitoring, it is also within the scope of
the invention to monitor the functions of the sensors used, in
particular as part of a plausibility check. For example, the
pressure sensor 19 located between temporary store 18 and metering
valve 21 can be checked by observing the correlation in the
pressure rise during filling of the temporary store 18,
specifically by comparison with a pressure curve stored in the
evaluation and control unit 8.
With regard to the second pressure sensor 22, which is located
downstream of the metering valve 21, a functional check is made
possible by the fact that, when the metering valve 21 is closed,
the pressure p.sub.2 indicated via the pressure sensor 22 is
compared with the exhaust-gas back pressure which is recorded on
the engine side and is measured upstream of the catalytic converter
4. If no pressure compensation is established within a
predetermined time, there is a malfunction. The malfunctions are
indicated and, in the event of a malfunction in the pressure sensor
19 located upstream of the metering valve 21, it is also
recommended to close the shut-off valve 17, because the
pressure-compensating function of the temporary store is otherwise
not ensured.
Furthermore, it is also within the scope of the present invention
to monitor the metering valve 21 and the shut-off valve 17 to
establish whether they are leaktight. For this purpose, in a
similar way to the detection of any leaks between shut-off valve 17
and metering valve 21, the leaktightness of metering valve 21 and
shut-off valve 17 can be checked by observing the pressure as a
function of time, with the temporary store 18 filled. If a pressure
deviation which can be detected as a fault is recorded, the test
operation can be repeated with the shut-off valve 17 open and the
vessel valve 14 closed, so that the fault must be at the metering
valve 21 if a relevant pressure deviation is found once again. In a
similar manner, the leaktightness of the vessel valve 14 can be
checked and monitored, even if a plurality of pressure vessels 7
are used in an alternating-cylinder concept.
Therefore, the present invention provides a device 9 and method for
exhaust-gas purification involving reduction of nitrogen oxides
which are present in the exhaust gas from internal combustion
engines 1 by gaseous ammonia using an SCR catalytic converter 4.
The present invention is distinguished by a simple structure, good
control options and a very extensive and simple monitoring concept,
in which the functions of the device 9 are monitored with regard to
their line paths with connections, valves and sensors by referring
to these elements themselves using suitable control circuitry via
the evaluation and control unit 8.
The foregoing disclosure has been set forth merely to illustrate
the invention and is not intended to be limiting. Since
modifications of the disclosed embodiments incorporating the spirit
and substance of the invention may occur to persons skilled in the
art, the invention should be construed to include everything within
the scope of the appended claims and equivalents thereof.
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